Carrier Aggregation is a way to bundle a number of wireless channels in order to achieve a larger aggregated bandwidth and hence a larger possible peak bitrate in cellular networks. Carrier Aggregation is defined as part of the LTE-Advanced standard in 3GPP Rel-10 [www.3gpp.org] as well as in the WiMAX (IEEE 802.16m) standard.
Carrier Aggregation is not limited to channels/bands which are adjacent, but inter-band Carrier Aggregation is also supported.
Due to the expected massive growth of mobile broadband data, cellular operators currently look at alternative solutions to manage the cost of their networks.
In contrast to the initial years of WLAN and cellular networks, where both technologies co-existed without any interaction, the standardisation organisations have developed a number of enhancements to interconnect WLAN with cellular technologies. For example I-WLAN (Interworked-Wireless LAN) has been added by 3GPP in its Rel-7 to provide access via WLAN and a gateway to the 3GPP system. As an enhancement to this connection between WLAN and 3GPP systems with the event of Evolved Packet System (EPS), the so-called “untrusted access” using PMIP/GTP (Proxy Mobile Internet Protocol/General Packet Radio Service (GPRS Tunnelling Protocol) or Proxy Mobile IPv6 (PMIPv6) via the S2b interface has been introduced. Even further interoperability between WLAN and Evolved Packet System (EPS) has been defined in 3GPP Rel-10 with the work on “IP flow mobility”, which allows concurrent operation of a single terminal using WLAN access on the one hand, while being connected via UMTS or LTE radio network on the other. Selective IP flow routing enables an improved user experience as depending on the Quality-of-Service (QoS) or operator requirements, Internet Protocol (IP) flows can be routed selectively on the one or the other radio access. Furthermore this feature package also allows seamless authentication and seamless mobility between cellular and WLAN radio networks.
However, there is still a separation in the Internet Protocol (IP) flows between the integration between WLAN access and UMTS/LTE.